1. Field of the Invention
The present invention concerns a tool for applying surface coated abrasives for use on a machine for abrasion machining of cylindrical surfaces on workpieces, especially crankshaft journals and crankpins.
2. Description of the Prior Art
Machines of this type described, for example, in patent application EP-A-0 366 506 comprise, for each bearing surface to be machined on a workpiece, a pivoting arm mobile vertically and carrying three surface coated abrasive application pads disposed substantially at the three corners of an equilateral triangle. A first of the three pads is mounted at a median top position on the arm and the other two in lateral bottom positions on two jaws articulated to the arm and coupled so that they can be clamped together by synchronous pivoting in opposite directions due to the action of common maneuvering means. The arm is moved vertically by a balancing cylinder with regulated feed pressure. When the jaws are clamped the three pads apply surface coated abrasives to the bearing surface to be machined with a uniform pressure.
In the prior art machines the pads which apply the surface coated abrasives have an application surface in the shape of a circular arc subtending a relatively small angle, usually less than 30.degree.. These tools give good results in terms of the bearing surface finish.
For honing cylindrical bearing surfaces on workpieces "hones" are used whose surface in contact with the bearing surface to be machined is in the shape of a circular arc subtending an angle of up to 60.degree.. The hones wear asymmetrically during machining so that in practise they exert pressure and therefore their action of honing the cylindrical bearing surface on the workpiece over an angle significantly less than 60.degree..
In other prior art machines using surface coated abrasives the tools in contact with each cylindrical bearing surface to be machined comprise two opposed surface coated abrasive application pads disposed on two jaws of a clamp, each pad having a circular arc shape application surface subtending an angle of almost 180.degree.. The drawback of these prior art pads used in pairs is poor distribution of the application pressure. The pressure is inevitably concentrated in the median part of the circumferential length of the circular arc shaped surface of the two opposed pads.
None of the prior art tools constitutes an entirely satisfactory response to the severe demands in terms of precision that apply nowadays, for example with respect to the absence of shape defects and to the straightness of crankshaft journals and crankpins.
The present invention is directed to a tool for applying surface coated abrasives enabling more accurate machining by abrasion of cylindrical bearing surfaces on workpieces such as crankshaft journals and crankpins.